If a pilot's personality changes drastically, "we're going to pull him aside. Management will get involved and not in a hostile fashion. We work with people."

Update at 5:09 p.m. ET: The FAA requires commercial pilots to be medically certified every year if they are younger than 40 or every six months if older, USA TODAY's Bart Jansen reports.

A pilot must have a physical exam by an FAA-designated medical examiner, who assesses the pilot's psychological condition as part of the checkup. The examiner can order additional psychological testing.

"I knew there were about 130 people on the plane ... families, kids ... and I thought, this is not going to happen on my plane," said David Gonzalez, 50, a former New York City Department of Corrections officer. " 'We got to get this plane down. This guy is nuts,' " he recalled thinking.

Gonzalez described putting the pilot in a chokehold. The pilot passed out about three minutes later, and other male passengers helped subdue him.

Gonzalez, a father of five, now works for a security and surveillance company and was on his way to Las Vegas for an annual security show.

He and his family live in the Pocono Mountains in Pennsylvania, he told ABC.

Update at 4:32 p.m. ET: The 135 passengers are still at the Amarillo airport, and JetBlue is sending another aircraft for them, CBSDFW-TV reports. The Federal Aviation Administration has released this statement:

This morning, at approximately 9:53 a.m. Central Time, a Jet Blue flight en route to Las Vegas from New York JFK International Airport was diverted to Amarillo Rick Husband International Airport for an onboard medical emergency.

Preliminary information indicates that after landing, it was learned that the co-pilot became concerned that the captain exhibited erratic behavior during the flight. The captain had exited the cockpit during the flight, after which the co-pilot locked the door. When the captain attempted to enter the locked cockpit, he was subdued by passengers. After the flight landed safely, local law enforcement secured the pilot without incident, and he was transported by ambulance for medical evaluation.

The aircraft was towed to the terminal building and the passengers were safely deplaned from the aircraft. Passengers are currently awaiting continuation of their travel to Las Vegas.

The FBI, FAA, TSA and local law enforcement are coordinating on this incident.

Update at 4:17 p.m. ET: There are conflicting takeoff times for the plane, both attributed to JetBlue: 10:45 a.m., cited by the Amarillo paper and other news outlets, and 7:28 a.m. ET, delayed from a scheduled 6:55 a.m. departure.

Update at 4:04 p.m. ET: John Cox, a former pilot who is now a safety expert, tells USA TODAY's Bart Jansen that the other pilot on the flight could have landed the plane safely, even without any assistance from the off-duty captain. Cox said crewmembers are trained to restrain combative passengers under a program that could have applied to the pilot.

"The same training to restrain an abusive passenger that presents a physical threat could be utilized against a crewmember," said Cox, president of Safety Operation Systems. "It was great that there was another captain that was on the flight that could assist the first officer. Had he not been there, though, the first officer is completely capable and trained to land the aircraft. There was never a risk to the passengers."

The nature of the "medical situation" is still not known. Passengers said the captain appeared to suffer some kind of panic attack, with one telling CNN the pilot asked to be restrained.

Update at 3:54 p.m. ET: One passenger said a former prison security guard grabbed the captain by the neck and choked him until he collapsed, the Globe-News says. The New York Daily News reports that a retired NYPD sergeant subdued the captain.

Update at 3:25 p.m. ET: An off-duty captain on the flight took over the pilot's duties "once on the ground," JetBlue said in a statement without elaborating, AP reports.

Update at 3:12 p.m. ET: The pilot went into a toilet, then emerged "shouting, 'Iraq, al-Qaeda, terrorism, we're all going down.' It seemed like he went crazy," said Gabriel Schonzeit, of New York City, who was seated in the third row.

Passengers said six to 10 travelers jumped the pilot and pinned him to the floor. Schonzeit described him as "a very large man, bigger than me." Schonzeit is 6 feet, 3 inches and weighs 250 pounds.

The pilot has not been identified.

The flight was taking passengers to Las Vegas for a security convention, the Globe-News says.

Original posts by Douglas Stanglin:

Update at 3:03 p.m. ET: CNN quotes one passenger, Tom Murphy, as saying that the captain had come into the cabin and initially tried to break into a locked bathroom, then banged on the cockpit door.

At one point, Murphy tells CNN, the flight attendants tried to take the pilot to the back of the plane, but he broke free and ran to the front, threatening to blow up the plane and saying there was a bomb on board.

Original post: Flight 191 had 135 passengers and five crewmembers when it took off from John F. Kennedy Airport at about 10:45 a.m., JetBlue said, according to the airline.

The Globe-News quotes Josh Redick, 41, of New York, as saying the crew kicked the pilot out of the cockpit, and he turned unruly and tried to use the intercom system, which had been disabled.

Heidi Karg tells CNN that there was a lot of commotion and that she heard the man she thinks was the captain shout the word "bomb."

JetBlue and Transportation Security Administration officials described the pilot as having a medical condition.

The pilot, who has not been identified, was transported to Northwest Texas Hospital, officials said.

"Another captain, traveling off duty on Flight 191, entered the flight deck prior to landing at Amarillo, and took over the duties of the ill crewmember once on the ground," the company said in a statement. "The aircraft arrived Amarillo at 10:11 a.m., and the crewmember was removed from the aircraft and taken to a local medical facility. "

The newspaper quotes TSA spokesman Luis Casanova as saying it "seems to be more of a medical issue than a security issue at this point."

One passenger told Fox 5 News the pilot was in the cabin trying to storm the cockpit.

"I saw a guy wearing a pilot's uniform run down the aisle screaming and yelling and banging on the cockpit door to let him in," the witness said.

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About Doug Stanglin

Doug is an unrepentant news junkie who loves breaking news and has been known to watch C-SPAN even on vacation. He has covered a wide range of domestic and international news stories, from prison riots in Oklahoma to the Moscow coup against Mikhail Gorbachev. Doug previously served as foreign editor at USA TODAY. More about Doug

About Michael Winter

Michael Winter has been a daily contributor to On Deadline since its debut in January 2006. His journalism career began in the prehistoric Ink Era, and he was an early adapter at the dawn of the Digital Age. His varied experience includes editing at the San Jose Mercury News and The Philadelphia Inquirer.